AMPLIFICATION OF THE LAW OP POISMUILLE 35
• definite effect on the viscosity in an electrical field, which
elberger (1898) attempted to explain on the basis of
jsis. However, Pacher and Finazzi (1900) obtained results
were contrary to those of Duff and Quincke finding that
ing liquids under the action of an electrical field do not
o any sensible change in viscosity. Ercolini (1903) made
aents along the same line and concluded that the effect
ss than his experimental error. He used petroleum
&y turpentine, olive oil, and vaseline. Carpini (1903)
*ed the viscosity of magnetic liquids in a magnetic field but
no certain effect. Koch (1911) tried the effect of oxygen
rogen polarisation at the boundary using a platinum tube
. oscillating copper disk. No change in the viscosity was
3d and Koch regards this as strong evidence against
g. Bonceray (1911) has studied the effect of surface
L.
$e results seem to make it quite certain that, whether
uid wets the solid or not, there is no measurable difference
:ix the velocity of the solid and of the liquid immediately in
t with it, at least so long as the flow is linear.
Transition from Linear to Turbulent Flow.—It is well
that the formulas which have "been discussed do not
to trie ordinary flow of liquids in pipes. Under ordinary
,ons we know that the flow is undulatory, instead of being
is is assumed in the simple laws of motion. It is important
7e know under what conditions these sinuous motions
• so that they may be properly taken into account or
:d against. An extended study of the flow of water in
taving a diameter varying from 0.14 to 50 cm was made by
(1858). He found the hydraulic resistance proportional
rriere n had a value nearly equal to 2 (1.92). He saw more
• than any of his predecessors that hydraulic flow is very
at in character from the viscous flow studied by Poiseuille,
lie viscous resistance is proportional to the flrst power of
sari velocity (I). Darcy paid little attention to the tern-
re at which his experiments were carried out, probably as
Ids remarks, because "the resistance after eddies have
established is nearly, if not quite, independent of the
ty." Since Darcy's work was approved by the Academy